Training-related Decrease in Antagonist Muscles Activation is Associated with Increased Motor Cortex Activation: Evidence of Central Mechanisms for Control of Antagonist Muscles

During human contraction, net joint torque production involves the contribution of the antagonist muscles. Their activation protects the articulations and facilitates movement accuracy, but despite these fundamental roles, little is known about the brain mechanisms underlying their control. In view of previous studies that showed lesser antagonist muscles activation in participants engaged in regular strength training (ST) than in participants actively engaged in endurance disciplines (ED), we used this between-group comparison to investigate the possible role of motor cortex activity on the control of antagonist muscles. Electroencephalographic (EEG) and electromyographic (EMG) activity as well as the net joint torque were recorded, while ten ST and eleven ED participants performed isometric knee muscles exertions at different force levels. EEG data showed a linear increase in the suppression of cortical oscillations in the 21-31 Hz frequency band with increasing force level in ST but not in ED participants. This effect was associated with lesser EMG activation of the antagonist muscles in ST than in ED participants, the difference between groups also increasing with the force level. Both effects were found specifically during flexion exertions, indicating that ST participants developed sharp central adaptations to control the antagonist muscles involved as prime movers in their usual training task. This result suggests that the cortical adaptations induced by regular strength training could exert a specific encoding of the antagonist muscles, leading to the minimization of their activation and improved energetic efficiency of the muscle contraction.